Re: [PATCH 5/8] tty: serial: samsung: Enable console as module

Sam Protsenko
2021-11-29T22:44:31Z

On Mon, 29 Nov 2021 at 10:52, Krzysztof Kozlowski
<krzysztof.kozlowski@canonical.com> wrote:
>
> On 27/11/2021 23:32, Sam Protsenko wrote:
> > Enable serial driver to be built as a module. To do so, init the console
> > support on driver/module load instead of using console_initcall().
> >
> > This is needed for proper support of USIv2 driver (which can be built as
> > a module, which in turn makes SERIAL_SAMSUNG be a module too). It also
> > might be useful for Android GKI modularization efforts.
> >
> > Inspired by commit 87a0b9f98ac5 ("tty: serial: meson: enable console as
> > module").
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
> > ---
> > drivers/tty/serial/Kconfig | 2 +-
> > drivers/tty/serial/samsung_tty.c | 21 +++++++++++++++++++--
> > 2 files changed, 20 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> > index fc543ac97c13..0e5ccb25bdb1 100644
> > --- a/drivers/tty/serial/Kconfig
> > +++ b/drivers/tty/serial/Kconfig
> > @@ -263,7 +263,7 @@ config SERIAL_SAMSUNG_UARTS
> >
> > config SERIAL_SAMSUNG_CONSOLE
> > bool "Support for console on Samsung SoC serial port"
> > - depends on SERIAL_SAMSUNG=y
> > + depends on SERIAL_SAMSUNG
> > select SERIAL_CORE_CONSOLE
> > select SERIAL_EARLYCON
> > help
> > diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> > index f986a9253dc8..92a63e9392ed 100644
> > --- a/drivers/tty/serial/samsung_tty.c
> > +++ b/drivers/tty/serial/samsung_tty.c
> > @@ -1720,10 +1720,10 @@ static int __init s3c24xx_serial_console_init(void)
> > register_console(&s3c24xx_serial_console);
> > return 0;
> > }
> > -console_initcall(s3c24xx_serial_console_init);
> >
> > #define S3C24XX_SERIAL_CONSOLE &s3c24xx_serial_console
> > #else
> > +static inline int s3c24xx_serial_console_init(void) { return 0; }
> > #define S3C24XX_SERIAL_CONSOLE NULL
> > #endif
> >
> > @@ -2898,7 +2898,24 @@ static struct platform_driver samsung_serial_driver = {
> > },
> > };
> >
> > -module_platform_driver(samsung_serial_driver);
> > +static int __init samsung_serial_init(void)
> > +{
> > + int ret;
> > +
> > + ret = s3c24xx_serial_console_init();
> > + if (ret)
> > + return ret;
>
> This will trigger warns on module re-loading, won't it? Either suppress
> unbind or cleanup in module exit.
>

I guess that's already taken care of in samsung_serial_remove(): it's
doing uart_remove_one_port(), which in turn does unregister_console().
So I don't think anything extra should be done on module exit. Or I'm
missing something?

That case (unload/load) actually doesn't work well in my case: serial
console doesn't work after doing "modprobe -r samsung_tty; modprobe
samsung_tty" (but it works fine e.g. in case of i2c_exynos5 driver).
Not sure what is wrong, but I can see that my board keeps running
(heartbeat LED is still blinking). Not even sure if that use case
(unload/load) was ever functional before.

Anyway, please let me know if you think something should be done about
this particular patch. Right now I don't see anything missing.

> > +
> > + return platform_driver_register(&samsung_serial_driver);
> > +}
> > +
> > +static void __exit samsung_serial_exit(void)
> > +{
> > + platform_driver_unregister(&samsung_serial_driver);
> > +}
> > +
> > +module_init(samsung_serial_init);
> > +module_exit(samsung_serial_exit);
> >
> > #ifdef CONFIG_SERIAL_SAMSUNG_CONSOLE
> > /*
> >
>
>
> Best regards,
> Krzysztof